1. Field of the Invention
The present invention relates to an ultrasound diagnostics system for obtaining a tomographic image of an organism by transmitting a plurality of ultrasonic pulses to the organism at a focal distance and receiving a plurality of echo signals reflected on the organism while scanning the organism.
2. Description of the Related Art
2.1. Previously Proposed Art
A tomographic image of an organism is obtained by using an ultrasound diagnostics system in which ultrasonic pulses are transmitted to an organism at a focal distance and receiving a plurality of echo signals reflected on the organism while scanning the organism.
FIG. 1 is a block diagram of a conventional ultrasound diagnostics system.
As shown in FIG. 4, a conventional ultrasound diagnostics system 11 comprises an ultrasound probe 12 having a plurality of micro-piezoelectric transducers 13 for transmitting a plurality of ultrasonic pulses from the transducers 13 to an organism while scanning the organism and receiving a plurality of echo signals reflected in the organism to the transducers 13, an actuating unit 14 having a plurality of pulse oscillators 15 for actuating the micro-piezoelectric transducers 13 of the ultrasound probe 12 with a plurality of actuating pulses transmitted from the pulse oscillators 15, a transmitted ultrasonic pulse focusing unit 16 having a plurality of delaying circuits 17 for transmitting a plurality of delaying pulses Tx generated in the delaying units 17 to the pulse oscillators 15 to delay the generation of the actuating pulses for the purpose of converging the ultrasonic pulses transmitted from the micro-piezoelectric transducers 13 to a focal point of the organism, a trigger unit 18 for transmitting a trigger pulse Tg to the transmitted ultrasonic pulse focusing unit 16 to trigger the generation of the delaying pulses Tx, a focus memory 19 for storing a plurality of groups of delay time data Dn (n=1 to N) corresponding to a plurality of focal distances fn, an inputting unit 20 for inputting a piece of input information indicating a desired focal distance fi, a focal distance setting unit 21 for reading a group of delay time data Di from the focus memory 19 according to the input information and transmitting the group of delay time data Di to the transmitted ultrasonic pulse focusing unit 16 to set the convergence of the ultrasonic pulses at a focal point of the organism corresponding to the focal distance fi, a received echo signal focusing unit 22 having a plurality of delaying circuits 23 and an adder 24 for delaying the echo signals transmitted from the micro-piezoelectric transducers 13 of the ultrasound probe 12 at a plurality of time differences in the delaying circuits 23 to converge the echo signals at a fixed time and adding the echo signals together in the adder 24 to produce a summed echo signal Se, a signal processing unit 25 for performing a logarithmic transformation for the summed echo signal Se obtained in the received echo signal focusing unit 22 and detecting a phase of the summed echo signal Se to produce a piece of tomographic image data indicating a portion of a tomographic image, a scanning transformation unit 26 having two-dimensional memories 27 for writing the piece of tomographic image data transmitted from the signal processing unit 25 in each of the two-dimensional memories 27 according to a scanning line of the ultrasonic pulses and producing an image signal Sv indicating the tomographic image expressed by a displaying format such as a television format, and a displaying unit 28 for displaying the ultrasound tomographic image of the organism according to the image signal Sv transmitted from the two-dimensional memories 27.
In the above configuration, an operation in the conventional ultrasound diagnostics system 11 is described.
A group of micro-piezoelectric transducers 13, a group of pulse oscillators 15, a group of delaying circuits 17 and a group of delaying circuits 23 respectively correspond to a plurality of channels, and an operation among the ultrasound probe 12, the actuating unit 14, the transmitted ultrasonic pulse focusing unit 16 and the received echo signal focusing unit 22 is performed for each of the channels.
When an operator inputs a piece of input information indicating a desired focal distance fi, a group of delay time data Di corresponding to the focal distance fi is read out by the focal distance setting unit 21, and a delaying pulse Tx is generated in each of the delaying circuits 17 according to the group of delay time data Di in the pulse focusing unit 16 in synchronization with a trigger pulse Tg transmitted from the trigger unit 18. Thereafter, an actuating pulse is generated in each of the pulse oscillators 15 when the delaying pulses Tx are received by the actuating unit 14 at different times, and the micro-piezoelectric transducers 13 of the ultrasound probe 12 are actuated by the actuating pulses. Therefore, a plurality of ultrasonic pulses delayed by prescribed different times are output from the transducers 13, and the delayed ultrasonic pulses simultaneously reach a focal point of an organism corresponding to the focal distance fi. That is, the delayed ultrasonic pulses are converged at the focal point of the organism.
Thereafter, an echo signal reflected at the focal point of the organism is generated for each of the delayed ultrasonic pulses, and the echo signals are received by the transducers 13 at prescribed different times. Thereafter, the echo signals are delayed in the delaying circuits 23 of the received echo signal focusing unit 22 and are added up together in the adder 24 to produce a summed echo signal Se. Thereafter, in the signal processing unit 25, the summed echo signal Se is logarithmic-transformed, and the transformed signal is phase-detected in amplitude modulation to produce a piece of tomographic image data. Therefore, pieces of tomographic image data indicating a portion of tomographic image on a scanning line can be produced by the signal processing unit 25 when the group of ultrasonic pulses is transmitted to a plurality of focal points of the organism along the scanning line at the desired focal distance fi. The pieces of tomographic image data are transmitted one after another to the scanning transformation unit 26.
In the unit 26, each of the tomographic image data is written in a corresponding two-dimensional memory 27. In this case, an address of the corresponding two-dimensional memory 27 is indicated by an address signal output from a writing address counter 29 to which the trigger pulse Tg of the trigger unit 18 is input. Therefore, the pieces of tomographic image data are written in a memory region of the two-dimension al memories 27 corresponding to the desired focal distance fi in synchronization with the trigger pulses Tg. Therefore, when a group of ultrasonic pulses is transmitted to the organism at each of a plurality of focal distances, pieces of tomographic image data indicating a frame of tomographic image are produced by the signal processing unit 25 and are written in all of the two-dimensional memories 27 of the scanning transformation unit 26.
Thereafter, the tomographic image data stored in the two-dimensional memories 27 are read out one after another according to address signals output from a reading-out address counter 30 and are transformed to a format such as a television format represented by the National Television System Committee. The tomographic image data indicating the tomographic image expressed by the television format are output to the displaying unit 28. Also, a synchronizing signal is output from the address counter 30 to the displaying unit 28. Therefore, the tomographic image is displayed in synchronization with the synchronizing signal by the displaying unit 28.
FIG. 2(A) shows the two-dimensional memories 27 divided into four memory regions R1 to R4.
In cases where pieces of tomographic image data corresponding to only one focal distance f1 are produced in the ultrasound diagnostics system 11, the tomographic image data indicating one tomographic image corresponding to the focal distance f1 are written in the entire four memory regions R1 to R4 of the two-dimensional memories 27. Also, in cases where pieces of tomographic image data corresponding to a first focal distance f1 and a second focal distance f2 larger than the first focal distance f1 are produced in the ultrasound diagnostics system 11, the tomographic image data indicating a part of tomographic image corresponding to the first focal distance f1 are written in the first and second memory regions R1 and R2 of the two-dimensional memories 27, and the tomographic image data indicating a remaining part of tomographic image corresponding to the second focal distance f2 are written in the third and fourth memory regions R3 and R4 of the two-dimensional memories 27. Therefore, one tomographic image corresponding to the focal distances f1 and f2 is obtained. Also, in cases where pieces of tomographic image data corresponding to four focal distances f1 to f4 (f1&lt;f2&lt;f3&lt;f4) are produced in the ultrasound diagnostics system 11, the tomographic image data indicating a first part of tomographic image corresponding to the first focal distance f1 are written in the first memory region R1, the tomographic image data indicating a second part of tomographic image corresponding to the second focal distance f2 are written in the second memory region R2, the tomographic image data indicating a third part of tomographic image corresponding to the third focal distance f3 are written in the third memory region R3, and the tomographic image data indicating a fourth part of tomographic image corresponding to the fourth focal distance f4 are written in the fourth memory region R4. Therefore, one tomographic image corresponding to the four focal distances f1 to f4 is obtained.
As shown in FIG. 2(B), a beam width and a beam intensity in a beam of the ultrasonic pulses converged by the transmitted ultrasonic pulse focusing unit 16 varies with the focal distance fi (or a converging depth). Therefore, a position of each boundary line between two memory regions adjacent to each other is determined to almost equalize a beam width and a beam intensity corresponding to one memory region with those corresponding to the other memory region at the boundary line.
Also, when an operator focuses the ultrasonic pulses on a remarked focal point of the organism to produce a tomographic image corresponding to one focal distance or two or more focal distances, one group of delay time data or a combination of two or more groups of delay time data is selected by inputting a piece of input information to the input unit 20 by the operator.
Therefore, a plurality of groups of delay time data Dn corresponding to the focal distances fn are stored in advance in the focus memory 19, one group of delay time data or a combination of two or more groups of delay time data is selected, and the ultrasonic pulses are converged at a remarked focal point of the organism. Accordingly, a tomographic image having a superior focus orientation resolution can be obtained in the conventional ultrasound diagnostics system 11.
2.2. Problems to be Solved by the Invention
However, in cases where a focal distance is selected from among a large number of focal distances corresponding to focal points widely ranging from a shallow portion of the organism to a deep portion of the organism, the number of groups of delay time data required to be stored in advance in the focus memory 19 is extremely increased.
Also, in cases where a tomographic image is produced by converging a group of ultrasonic pulses at many focal points ranging in a depth direction from a shallow portion of the organism to a deep portion of the organism, a focal distance setting operation is required for each of the focal point. Therefore, the number of focal distance setting operations required to produce a frame of tomographic image is extremely increased, and there is a drawback that a frame rate of tomographic images is lowered.